ELECTROLYTIC DEVICE FOR GENERATION OF pH-CONTROLLED HYPOHALOUS ACID AQUEOUS SOLUTIONS FOR DISINFECTANT APPLICATIONS

ABSTRACT

An electrolytic device for the generation of hypohalous acid in aqueous solutions includes at least a single liquid chamber for receiving an aqueous solution containing halide ions therein, the single liquid chamber having an exterior wall and a solid anode contained within to provide for the oxidation of the halide ions, which, in turn, provides for the formation of hypohalous acid in aqueous solution, and a gas permeable cathode forming a portion of the exterior wall of the single liquid chamber, the cathode providing for the reduction of oxygen to provide hydroxyl ions in solution within the single liquid chamber to mix with the products generated at the anode. An embodiment of the electrolytic device including an anolyte chamber and a catholyte chamber separated by an ionomeric membrane is also described, whereby the anolyte chamber further includes an outlet including a pH control for determining and regulating the pH of the exiting anolyte effluent to between about 4 and 9. The product is suitable for disinfectant applications including as a hand sanitizer.

TECHNICAL FIELD

The present invention relates to a method for forming hypohalous acidand further relates to at least a single liquid chamber electrolyticdevice for generation of pH-controlled hypohalous acid aqueous solutionsfor disinfectant applications. This method and device has the advantagewhereby the pH of the solution is regulated and optimized. Such a methodand device is particularly useful for preparing hypochlorous acid.Specifically, the resultant effluent exiting the device, which may beHClO in aqueous solution, is suitable for use in hand sanitizers.

BACKGROUND OF THE INVENTION

Others have attempted to produce hypohalous acids using a variety ofmethods. For example, one method of producing low-chloride aqueoussolutions of hypochlorous acid (HClO) includes spraying fine droplets ofaqueous alkali metal hydroxides or alkaline earth metal hydroxides in areactor dryer with chlorine gas to make hypochlorous acid gas and solidmetal chloride. Creating the spray of fine droplets requires highpressures, and thus, a high energy input. The hypochlorous acid gas isthen condensed along with the water vapor, requiring refrigerationequipment to achieve condensing temperatures, to produce concentratedhypochlorous acid. Disadvantages of this process include difficulty inhandling the solid salt, high chlorine ratios, and energy inefficiency.

Another process which shares the aforementioned disadvantages for makingaqueous hypochlorous acid includes spraying a solution of alkali metalhydroxide into a chlorine atmosphere resulting in HClO vaporization anda dry solid salt. With this process, aqueous HClO solution is producedby absorption of the HClO in water as opposed to the condensation of theHClO and water vapor.

Still another process uses an organic solvent to extract HClO from abrine solution. This process suffers from a need to further remove theHClO from the organic solvent to produce an aqueous HClO solution, aneed to remove residual solvent from the brine solution, and undesirablereactions of HClO with the organic solvent.

Despite the several known processes for producing hypochlorous acid,there remains a need for a quick, safe, and efficient process forproducing hypochlorous acid solutions suitable for disinfectantapplications. Therefore, methods which do not require handling of solidsalt by-products or chlorine gas input have been sought, as have moreenergy efficient methods been desired which do not require largeheating/cooling cycles or high pressure on the liquid feed.

One method for producing hypochlorous acid solutions suitable for use asa disinfectant in food processing describes controlling thehypochlorite/hypochlorous acid balance of a stream by mixing liquid acidwith a pressurized carrier stream which has been chlorinated by theaddition of a chlorination agent. By decreasing the pH of the liquidstream, the relative ratio of hypochlorous acid to hypochlorite of theliquid stream is increased. This process allowed for the manipulation ofthe pressurized streams in order to produce specific concentrations ofhypochlorous acid providing greater control over the reaction process;however this process necessitates the introduction of a gaseous speciesother than air at preferred elevated temperatures.

Electrolytic cells have been utilized in prior inventions as related toproduction of acidic liquids. One such described invention provides anelectrolytic cell and process for the production of hydrogen peroxidesolution and hypohalide by electrolysis, whereby hypohalide and hydrogenperoxide are produced in the anode chamber and the cathode chamber,respectively. The invention specifically relates to a seawater treatmentmethod where both the desired products hydrogen peroxide andhypochlorous acid are reintroduced into the seawater to efficientlytreat the water. However, the invention necessitates the use of a dualchamber device, and hydrogen peroxide would not be suitable for a dailyhand sanitizing formulation.

Electrochemical devices have also been used previously to produce strongacid sterilizing liquids. One such device for use in water treatmentfacilities utilizes an apparatus for generating and dispensing a strongacid sterilizing liquid which contains hypochlorous acid at lowconcentrations and whose pH is 3 or less. In that apparatus, salt wateris passed through a channel formed between a positive electrode plateand a negative electrode plate disposed to face opposite surfaces of abarrier membrane in which DC voltage is applied between the electrodesto electrolyze the salt water. The barrier membrane prevents the mixingof the products at the positive electrode and the products at thenegative electrode. Acid liquid containing hypochlorous acid can beobtained by taking the aqueous solution flowing through the spacebetween the barrier membrane and the positive electrode out of theelectrolytic cell.

In another method directed toward obtaining a low pH aqueous acidsolution, also using a two-chamber-type electrolytic cell device, astrong acid water containing a reduced amount of chloride for use insterilization is produced whereby chloride ions are oxidized at theanode. With this apparatus, as with the previously described invention,the end product is desired to have a pH less than 3 and therefore is notsuitable for a daily hand sanitizing formulation.

Chlorination is long known as a method for killing undesirablemicroorganisms. Chlorine may be provided in multiple forms includingchlorine gas (Cl₂), a relatively cheap and highly effectiveantimicrobial agent; however, it is also a highly toxic and corrosivegas. Hypochlorites, such as NaOCl or Ca(OCl)₂, are a much saferalternative, but are considerably more expensive than gaseous chlorine.Finally, hypochlorite solutions (i.e., bleach) may also be utilized;however, these are rarely used in large scale applications because theyare bulky and hazardous. Regardless of the chlorine source, hypochlorousacid (HClO) and the hypochlorite ion (OCl⁻) are the final desirableantimicrobial products. In any application for a hand sanitizer,however, hypochlorous acid is preferred for safe use in contact withhuman skin.

Beyond safety, the bactericidal activity of an aqueous solution ofhypochlorous acid needs to be considered, particularly for use indisinfectant applications. The composition of an aqueous solution ofhypochlorous acid varies with the pH of the solution because the form ofchlorine compounds dissolved in the aqueous solution varies with pH. Atlow pH, typically above pH 3, HClO is the predominant form, while athigh pH, typically above pH 8, OCl⁻ predominates. The HClO form is about80 times more effective than OCl⁻ for killing microorganisms becauseHClO crosses cell membranes easier than the hypochlorite ion.

When the pH of an aqueous solution of hypochlorous acid is 8 or more, orthe aqueous solution of hypochlorous acid is alkaline, hypochlorous acidions (ClO⁻) having fairly low bactericidal activity are mainly presentin the aqueous solution. Thus, the bactericidal activity of an alkalineaqueous solution of hypochlorous acid is fairly low.

When the pH of aqueous solution of hypochlorous acid is 7 or less, orthe aqueous solution of hypochlorous acid is acidic, the amount ofhypochlorous acid (HClO) having a bactericidal activity 10 to 100 timeslarger than that of hypochlorite ions is larger than the amount ofhypochlorite ions. Thus, the bactericidal activity of an acidic aqueoussolution of hypochlorous acid is high.

When the pH of an aqueous solution of hypochlorous acid is between 3 and5.5, substantially 100% of the chlorine compound dissolved in theaqueous solution is hypochlorous acid. Thus, the bactericidal activityof the aqueous solution of hypochlorous acid becomes even higher.

When the pH of an aqueous solution of hypochlorous acid is 3 or less, apart of the chlorine compound dissolved in the aqueous solution becomeschlorine gas (Cl₂) having yet higher bactericidal activity than that ofhypochlorous acid. Thus, the bactericidal activity of the aqueoussolution of hypochlorous acid becomes even higher. However, human skinmay be damaged by application of acid sterilizing liquid of such a lowpH.

It would be desirable to control the pH of the chlorinated solution toincrease the antimicrobial effectiveness of the chlorination process andalso to ensure safety for uses such as hand sanitizer. Previousprocesses and systems for adjusting the pH of a water stream have beendescribed. These processes include using carbon dioxide by injectioninto water by a direct gas feed, or bubbler; or in another method forinjecting carbon dioxide into water by aspirating the carbon dioxideinto a stream of water using a Venturi-type eductor. It is, however,difficult to control the efficiency of the carbon dioxide gas usage andthese processes are inherently inefficient.

SUMMARY OF THE INVENTION

In the present device, an aqueous solution containing halide ions isintroduced into an electrolytic device for generation of pH-controlledhypohalous acid aqueous solutions, whereby at least a single liquidchamber may be utilized in which reactions are taking place at theinterface between the each of the electrodes and the electrolytesolution to produce an effluent of HClO in aqueous solution. Asreactions are taking place in the presence of excess water, thereactions occurring in the single liquid chamber release an effluentwhich may be monitored for pH, a desired pH range between about 4 and 9.This method and device has an advantage in that storage of gaseousspecies, such as chlorine gas, is not needed. Also, the sourceelectrolyte is economical and safe for handling, while the end productmay be directly used for disinfectant purposes at a controlled pH levelsuitable for use as a hand sanitizer without irritation or damage.

More specifically, the present invention provides an electrolytic devicefor the generation of hypohalous acid in aqueous solutions, the devicecomprising: a single liquid chamber having an inlet for receiving anaqueous solution containing halide ions, the single liquid chamberhaving an exterior wall and a solid anode contained within the singleliquid chamber providing for the oxidation of the halide ions to providean aqueous solution of hypohalous acid; and a gas permeable cathodeforming at least a portion of the exterior wall of the single liquidchamber, the cathode providing for the reduction of oxygen to providehydroxyl ions within the single liquid chamber to mix with thehypohalous acid produced at the anode, the cathode having a hydrophobicsurface for receiving oxygen from outside the single liquid chamber anda hydrophilic surface in contact with the electrolyte solution allowingfor reduction of dioxygen.

Further, the present invention provides an electrolytic device for thegeneration of hypohalous acid in aqueous solutions, the devicecomprising: an anolyte chamber having an inlet for receiving an aqueoussolution containing halide ions, the anolyte chamber having an exteriorwall and a solid anode contained within the anolyte chamber providingfor the oxidation of the halide ions to provide an anolyte effluent ofhypohalous acid in aqueous solution; a catholyte chamber having an inletfor receiving an aqueous electrolyte, wherein the catholyte chamber isdefined by at least one exterior wall or portion thereof comprising agas permeable cathode, the cathode having a hydrophobic surface forreceiving oxygen from outside the catholyte chamber and a hydrophilicsurface allowing for reduction of dioxygen; and an ionomeric membranefor partitioning the anolyte chamber from the catholyte chamber; whereinthe anolyte chamber further includes an outlet including a pH controlfor determining and regulating the pH of the exiting anolyte effluent tobetween about 4 and 9.

The present invention further provides a method for the generation ofhypohalous acid comprising: oxidizing halide ions in the presence ofwater within a single liquid chamber to form an aqueous solution ofhypohalous acid; feeding oxygen through a gas permeable cathode toreduce the oxygen in the presence of water to form hydroxyl ions,wherein the gas permeable cathode forms at least a portion of theexterior wall of the single liquid chamber; mixing the solutioncontaining the hydroxyl ions in an amount sufficient to complete theelectrical circuit within the device and to produce hypohalous acid;determining the pH of the hypohalous acid to ensure that the pH isbetween about 4 and 9; and removing the hypohalous acid.

In addition, the present invention further provides a method for thegeneration of hypohalous acid comprising: oxidizing halide ions in thepresence of water within an anolyte chamber to form an anolyte effluentcontaining hypohalous acid; feeding oxygen through a gas permeablecathode to reduce the oxygen in the presence of water to form acatholyte effluent containing hydroxyl ions, wherein the gas permeablecathode forms at least a portion of an exterior wall of a catholytechamber; mixing the hydroxyl ions in an amount sufficient to completethe electrical circuit within the device to produce hypohalous acid;controlling the pH of the hypohalous acid to ensure that the pH isbetween about 4 and 9; and removing the hypohalous acid.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example and to make the description more clear, reference ismade to the accompanying drawings in which:

FIG. 1A is a schematic diagram illustrating the electrolytic deviceemployable in the process of the invention; and

FIG. 1B is a schematic diagram of the gas diffusion electrode used inthe electrolytic device employable in the process of the invention; and

FIG. 2 is a cross-sectional view of the device describing one embodimentincluding a single liquid chamber, a gas compartment, and a pH control;and

FIG. 3 is a three-dimensional representation of an alternativeembodiment of FIG. 2 whereby the gas compartment encircles the singleliquid chamber;

FIG. 4 is a three-dimensional representation of another alternativeembodiment of FIG. 2 whereby the single liquid chamber encircles the gascompartment; and

FIG. 5 is a cross-sectional view of an alternative embodiment of theinvention in which the dual chamber device includes an anolyte chamberand a catholyte chamber, wherein the gas permeable cathode serves as atleast a portion of the exterior wall of the catholyte chamber; thedevice further includes a recirculator and a pH control.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

Examples of the process of the invention for the production ofhypohalous acid in aqueous solution will be described hereinafter, butthe invention should not be construed as being limited thereto. Oneembodiment of the invention provides an electrolytic device 1 for theproduction of pH-regulated hypohalous acid aqueous solutions in a singleliquid chamber as shown in schematic diagram FIG. 1A. In theelectrolytic device 1 for use in the process of the invention, operationof the electrosynthetic reactor relies on the use of a DC constantcurrent power supply connected to the gas diffusion electrode 2 toinduce reduction of dioxygen to water and to the anode 3 to promoteoxidation of chloride ion to generate, for example, HClO. In thiselectrolytic cell, electricity is consumed to produce chemicals. In FIG.1B, the gas diffusion electrode 2, also known interchangeably herewithin as a gas permeable cathode, which acts as a current collector,has a hydrophobic surface 4 which faces air, or some gaseous source ofoxygen, on the outside to prevent liquid from filtering through thestructure. The gas diffusion electrode 2 further has a hydrophilicsurface 5 which faces the electrolyte and allows for theelectrocatalytic surface, where the actual reduction of dioxygen occurs,to form.

One representative form of an electrolytic device for the generation ofhypohalous acid is shown in the cross-sectional view of FIG. 2 and isdenoted by the numeral 10. Electrolytic device 10 includes a singleliquid chamber 12 and a gas compartment 14. In the invention, a halideion source in aqueous solution, such as NaCl solution or seawater,preferably freed of organic material thereby avoiding the oxidationreaction of organic material in the single liquid chamber, is suppliedto the electrolytic cell single liquid chamber 12 by way of a gravityfeed container or pump 16 through an inlet 18 for receiving aqueoussolutions containing halide ions. The gravity feed container 16 may bemade of any material, such as plastic or glass, which is non-reactivewith the buffered or unbuffered solution to be fed through theelectrosynthetic reactor. Valve 40 regulates flow through inlet 18feeding into the single liquid chamber 12.

The single liquid chamber 12 has a single liquid chamber exterior wall32 and a solid anode 20 contained within the single liquid chamber 12providing for the oxidation of the halide ions to produce hypohalousacid in aqueous solution. Alternatively, the solid anode 20 could be thewall, or a portion thereof, of the container, as it is not necessarythat the anode be immersed fully in the electrolyte.

The solid anode 20 used in the invention may be, for example, adimensionally stable anode (DSA), commercially available from a suppliersuch as De Nora Tech.

The gas permeable cathode 22 forms a portion of the single liquidchamber exterior wall 32 and provides for the reduction of oxygen toprovide hydroxyl ions in solution within the single liquid chamber whichwill then mix with the products of the anode. The cathode, having ahydrophobic surface for receiving oxygen from outside the single liquidchamber 12 and a hydrophilic surface allowing for reduction of dioxygen,used for this invention may be, for example, a gas diffusion electrode(GDE), commercially available from various suppliers including BASF FuelCell, Inc., containing high area carbon and high area Pt (platinum) asthe electrocatalyst. The use of an electrocatalyst is desired to reducethe overall power consumption of the electrolytic device by reducing theovervoltage required to reduce dioxygen to water. Otherelectrocatalysts, such as certain metals and oxides including speciesderived from the pyrolysis of certain organic materials, may be used aswell, and are generally to be used in porous form. Alternatively, thecatalyst may be supported on a plate, metal gauge, sintered powder orsintered metal fiber of a corrosion-resistant material such as stainlesssteel, zirconium, silver and carbon. By forming a hydrophobic sheet onthe side of the cathode opposite the single liquid chamber, access ofgas to the reactive surface can be enhanced.

In one alternative, the exterior of the single liquid chamber 12 asdefined by the gas permeable cathode 22 may be exposed to atmosphericair. In another embodiment, as shown in FIG. 2, the electrolytic device10 may further include an oxygen source 24 for providing oxygen to thegas permeable cathode 22 through a gas compartment 14. The oxygen source24 may be air, a commercially available oxygen cylinder, oxygen producedby the electrolysis of water in a separately installed electrolyticcell, or oxygen obtained by concentrating air by a PSA (pressure swingadsorption) device; and this oxygen source 24 may also include a pump toforce the oxygen toward the hydrophobic surface of the gas permeablecathode. The gas compartment 14 further includes an inlet 26 forreceiving oxygen through gas compartment exterior wall 30; whereby thegas compartment 14 has at least one gas compartment exterior wall 30that encloses the portion of the single liquid chamber exterior wallcomprised of the gas permeable cathode 22. An outlet 46 enables anyoverpressure of oxygen or air to leave the system.

Within the single liquid chamber, the products of the reactions at theinterfaces between the solid anode 20 and the gas permeable cathode 22combine to yield an exiting effluent hereby also referred to as a mixedeffluent.

In an example whereby the hypohalous acid produced is hypochlorous acid,and the halide ions are chloride ions, anodic oxidation takes place inthe single liquid chamber 12 to produce HClO via the oxidation ofchloride ion:

Cl⁻+H₂O→HClO+2e⁻+H⁺

While in the presence of water, the chlorine gas Cl₂ (which forms first)instantaneously transforms to HClO yielding results corresponding to theabove reaction. The gas permeable cathode 22 is responsible for thereduction of dioxygen to water according to this equation:

O₂+2H₂O+4e⁻→4OH⁻

The electrochemical reactions occur at or near the interfaces betweenthe electrodes and the electrolyte solution, not in the aqueous stream.The products are all water soluble.

The single liquid chamber 12 further includes an outlet 28, throughwhich the exiting mixed effluent leaves the single liquid chamber 12through single liquid chamber exterior wall 32, thereafter, the exitingeffluent passes through a pH sensing electrode or pH meter, denoted inFIG. 2 as 34, for determining the pH of the exited mixed effluent; thedesirable pH range for use as a hand sanitizer is between about 4 and 9.It may be appreciated that an error-sensing feedback device, or servo,may also be included to further aid in regulating the pH. The pH meterfor measuring the pH incorporates a valve 36, which may be anelectrically actuated valve, which then directs the exit stream out foruse as product when the effluent solution has a pH between about 4 and9.

In the embodiment as depicted in FIG. 2 and utilizing a single liquidchamber, it is possible to manage or control pH by altering the currentapplied by the DC constant current power supply to the circuit or,alternatively, by adding a buffering agent to adjust the pH of theelectrolyte solution halide feed as necessary.

Another representative form of an electrolytic device for the generationof hypohalous acid in the present invention is shown in thethree-dimensional view of FIG. 3 and denoted by the numeral 100. Theelectrolytic device is similarly equipped as is the single liquidchamber device of FIG. 2; however FIG. 3 demonstrates the configurationof the gas compartment 114 as is possible with a cylindrical gascompartment exterior wall 130. The single liquid chamber 112 may also becylindrical and is contained within the gas compartment 114. The singleliquid chamber 112 of the electrolytic cell 100 has a solid anode 120and a single liquid chamber exterior wall 132, which may also serve asthe interior wall of gas compartment 114. The single liquid chamberexterior wall 132 encloses the single liquid chamber 112, leaving anopening for the gas permeable cathode 122 to serve as a portion of thesingle liquid chamber exterior wall 132. As the solid anode 120 need notbe entirely immersed in the electrolyte contained within the singleliquid chamber 112, the solid anode 120 may alternatively serve as aportion of the wall as defined by single liquid chamber 112, providedthe anode is not placed at the same position in which the gas permeablecathode 122 is located.

As with the embodiment described in FIG. 2, the electrolytic device inFIG. 3 has a gravity feed container or pump 116 and an inlet 118 forfeeding halide ions in aqueous solution into the single liquid chamber112. A valve 140 further regulates flow from the gravity feed containeror pump 116 into the single liquid chamber 112. The mixed effluent exitsthe single liquid chamber through single liquid chamber exterior wall132 passing through an outlet 128 which leads the exit stream through apH sensing device or pH meter, denoted as 134 in FIG. 3, fordetermination of pH. Further, an error-sensing feedback device, orservo, may also be included. A valve 136 thereby directs the fluid outof the system for use as end product if desired pH range between about 4and 9 is attained. The gas compartment 114 has a gas compartmentexterior wall 130 which may serve to enclose the electrolytic device100. An inlet 126 feeds oxygen from an oxygen source 124 into the gascompartment 114 for reactions to occur at or near the interface with thegas permeable cathode 122; an outlet 146 allows for release of anyoverpressure of air or oxygen as necessary.

It is also possible, as with the device in FIG. 2, that alternativelythe device shown in FIG. 3 may be exposed to atmospheric air rather thanto utilize a gas compartment for introducing oxygen to the gas permeablecathode. Also, as with the single liquid chamber electrolytic cell ofFIG. 2, pH of the mixed effluent may best be controlled or optimized byadjusting the current applied by the DC constant current power supply tothe circuit, or alternatively by adding a buffering agent to adjust thepH of the electrolyte solution halide feed as necessary.

FIG. 4 is further an alternate representative form of an electrolyticdevice, denoted as device 200, for the generation of hypohalous acid inthe present invention and is shown in the three-dimensional view. Theelectrolytic device is similarly configured as is the single liquidchamber device of FIG. 3; however FIG. 4 demonstrates the positioning ofthe gas compartment 214 as the internal cylinder as is possible usingthe gas permeable cathode 222 as the external wall of the gascompartment. The single liquid chamber 212 may also be cylindrical andmay encircle the gas compartment 214; thereby the solid anode 220 formsthe single liquid chamber exterior wall while the gas permeable cathode222 serves as the interior wall of single liquid chamber.

As with the embodiment described in FIG. 3, the electrolytic device ofFIG. 4 has a gravity feed container or pump 216 and an inlet 218 forfeeding halide ions in aqueous solution into the single liquid chamber212. A valve 240 further regulates flow from the gravity feed containeror pump 216 into the single liquid chamber 212. The mixed effluent exitsthe single liquid chamber through the bottom face of single liquidchamber exterior wall 232 passing through an outlet 246 which leads theexit stream through a pH sensing device or pH meter 234, fordetermination of pH. An error-sensing feedback device, or servo, mayalso be included. A valve 236 thereby directs the fluid out of thesystem for use as end product if desired pH range between about 4 and 9is attained. The gas compartment 214 has a gas compartment exterior wall230 at top and bottom face and an inlet 226 which feeds oxygen from anoxygen source 224 into the gas compartment 214 for reactions to occur ator near the interface with the gas permeable cathode 222; an outlet 228allows for release of any overpressure of air or oxygen as necessary.

As with the single liquid chamber electrolytic cell devices of FIGS. 2and 3, pH of the mixed effluent may best be controlled or optimized byadjusting the current applied by the DC constant current power supply tothe circuit, or alternatively by adding a buffering agent to adjust thepH of the electrolyte solution halide feed as necessary.

FIG. 5 further describes another representative form of an electrolyticdevice 300 for the generation of hypohalous acid; whereby this dualchamber device has an anolyte chamber and a catholyte chamber. The cellhas an exterior wall 350, wherein the gas permeable cathode 322 ispositioned as at least a portion of the exterior wall of the catholytechamber 314. The electrolytic device 300 has an anolyte chamber 312which has an inlet 318 for receiving an aqueous solution of halide ionstherein. As shown in this embodiment, the anolyte chamber 312 has asolid anode 320 contained within the anolyte chamber providing for theoxidation of the halide ions to produce an anolyte effluent ofhypohalous acid in aqueous solution. The solid anode 320 may be placedwithin the anolyte chamber as shown or alternatively serve as animpermeable wall, or portion thereof, of the anolyte chamber, as it isnot necessary that the anode be fully immersed in the electrolyte.However, the solid anode 320 cannot form the part of the anolyte chamberwall that separates the anolyte chamber 312 from the catholyte chamber214.

In this dual chamber configuration, the gas permeable cathode 322 can bepositioned such that the catholyte chamber 314 has at least one wallthat includes at least, in part, the gas permeable cathode 322. Thecathode has a hydrophobic surface for receiving oxygen from outside thecatholyte chamber 314 and a hydrophilic surface allowing for reductionof dioxygen and for maintaining the aqueous-based catholyte effluentwithin the catholyte chamber 314 of the electrolytic device 300.

Furthermore, the cell as shown in FIG. 5 has an ionomeric membrane 344to partition the two liquid chambers, i.e., the anolyte chamber 312 andthe catholyte chamber 314. The membrane may be a neutral membrane or anion exchange membrane. The ionomeric membrane 344 may be an ion exchangemembrane made of synthetic polymer, such as Nafion® available fromDuPont, or alternatively a non ionomeric membrane of very fine porosityavailable from various sources, to prevent facile mixing of the anolyteand catholyte solutions. The Nafion membrane utilized in the presentembodiment allows the sodium cations (Na⁺) to transfer from the anolytechamber to the catholyte chamber with minimal electrical resistance,while minimizing back transfer of anions such as OH— from the catholytechamber. The use of ionomeric membrane 344 separating the anolytechamber 312 and the catholyte chamber 314 makes it possible to preventmixing of the liquids and also for the hypohalous acid to reach thecathode. While in operation, the anolyte chamber of the invention shouldcontain, in addition to the reactant chloride, HClO and not anysignificant amount of the reduction products of dioxygen, i.e.,catholyte effluent, that are produced in the catholyte chamber.

Separate inlets for feeding into the anolyte chamber 312 and catholytechamber 314 are maintained by inlet 318 and inlet 326 respectively.While there are many ways to accomplish feeding the cell, it may beviewed as depicted in FIG. 5 that the gravity feed container or pump 316introducing aqueous NaCl or halide ion containing solution to theanolyte chamber 312 could further include a source 324 for providingliquid water or another aqueous solution to the catholyte chamber 314.In this manner, the flow of liquids fed to the device may be managed bya valve 352 to regulate input to either the anolyte chamber 312 orcatholyte chamber 314 separately.

In the dual chamber embodiment of the invention as shown in FIG. 5, andwhereby the hypohalous acid produced is hypochlorous acid, and thehalide ions are chloride ions, anodic oxidation takes place in theanolyte chamber 312 to produce HClO via the oxidation of chloride ion:

Cl⁻+H₂O→+HClO+2e⁻+H⁺

While in the presence of water, chlorine gas Cl₂ (which forms first)instantaneously transforms to HClO yielding results corresponding to theabove reaction. Sodium cations (Na⁺) may pass from the anolyte chamber312 through the membrane 344 into the catholyte chamber 314. Thehydrophilic side of the gas permeable cathode 322 in the catholytechamber 314 is responsible for the reduction of dioxygen to wateraccording to this equation:

O₂+2H₂O+4e⁻→4OH⁻

The electrochemical reactions occur at or near the interfaces betweenthe electrodes and the electrolyte solution, not in the aqueous stream.The products are all water soluble. In this dual liquid chamber device,the sodium cations may migrate through the membrane 344 from the anolytechamber 312 to the catholyte chamber 314 with minimal electricalresistance. In the catholyte chamber 314, the sodium cations andhydroxyl groups remain as such dissolved in water to yield the catholyteeffluent.

In an alternative cylindrical embodiment not shown, drawn similarly tothe single chamber device concept shown in FIG. 3, the anolyte chamberof the dual chamber device may have an exterior wall, corresponding tothe wall 132 as described in FIG. 3, that is formed completely orsubstantially of the membrane. In such a cylindrical configuration ofthe dual chamber device, the gas permeable cathode may act as anexterior catholyte chamber wall, or a portion thereof, which wouldcorrespond similarly to the wall 130 as described in FIG. 3.

In the embodiment of the invention as depicted in FIG. 5, the anolytechamber 312 and catholyte chamber 314 further include outlets 328 and356, respectively, to progress the anolyte and catholyte effluentsthrough as desired to the exit stream at a controlled pH. Control of pHmay be accomplished by regulating the volume of catholyte effluentintroduced to the exit stream utilizing valve 348 which will bediscussed further below. The pH may be measured by a pH sensing deviceor pH meter 334 for determining pH, while valve 348 may be adjusted forregulating the pH of the exiting anolyte effluent to between about 4 and9.

The catholyte chamber 314 may contain unreacted aqueous solution, e.g.,water and/or reacted catholyte. The electrolytic device further includesan outlet 346 for releasing reacted catholyte effluent remaining in thecatholyte chamber 314. It will be appreciated that any reacted catholyteeffluent will be alkaline in nature. A valve 348 regulates flow of thecatholyte effluent through outlet 346 exiting from the catholytechamber; thereafter the exiting catholyte is mixed with the exitinganolyte effluent to form a mixed effluent of higher pH than of theanolyte effluent alone. The mixed effluent may be measured with pHsensing device or pH meter 334. The pH control, which may also include acomputer controlled servo, makes it possible to regulate the flow of theexiting liquid which passes through valve 336 to be in the desired rangeof pH between about 4 and 9. In practice, the pH meter 334 placed at theexit stream measures the pH of the exiting effluent. If the exitingeffluent is too acidic, valve 348 may be opened to allow catholyte toflow also, thereby, introducing the alkaline solution to the exitstream. Repeated adjustments to regulate the catholyte effluent flow tocombine with the effluent of the anolyte released may be made asnecessary until the exiting solution reaches the desired pH rangebetween about 4 and 9.

Further, the pH may be controlled by recirculating the anolyte or themixed anolyte and catholyte effluent through a recirculator 338 backinto inlet 318 for reintroduction into the anolyte chamber 312. Asdepicted in FIG. 5, the recirculator 338 has a valve 354 which allowsthe flow of the exiting anolyte effluent or mixed anolyte and catholyteeffluent to be redirected back into the anolyte chamber 312 when theanolyte effluent or mixed anolyte and catholyte effluent has a pH thatis greater than 9; or the flow may be redirected back into the anolytechamber when the exiting anolyte effluent or mixed anolyte and catholyteeffluent have a pH that is less than 4. In other words, to control pH,recirculating catholyte-containing effluent, or OH in aqueous solution,back into the anolyte chamber increases pH (to 5, to 6, to 7, up to 8).Alternatively, pH control may be achieved by recirculating exitinganolyte effluent back into the electrolyte within the anolyte chamber todecrease pH. Thereby attainment of the desired pH within the hypohalousacid solution end product may be in these ranges: preferred between 4-9;more preferred between 5-8; more preferred between 5-6; pKa of HClO is7.5 pH. To further control pH, the electrolytic device may allow for abuffering agent to be released through inlet valve 318 into the anolytechamber of aqueous solution containing halide ions. Also, as with thesingle liquid chamber design discussed previously, pH control of thedual chamber device may also be attained by optimizing current to thecircuit as applied by the DC constant current power.

Whereas FIG. 5 depicts a device open to atmospheric air to provide airto the gas permeable cathode 322 from outside of the inventive cell, itmay be alternatively possible to have a gas compartment to feed air oroxygen to the gas permeable cathode 322 similarly as described in FIGS.2 and 3. The oxygen source may include a pump to force the oxygen towardthe hydrophobic surface of the gas permeable cathode 322.

In all embodiments, the electrolytic cell 10, 100, 200, 300 ispreferably made of a glass lining material, carbon, orcorrosion-resistant titanium, stainless steel or PTFE resin from thestandpoint of durability and stability.

Examples of the process of the invention for the production of HClOsolution will be described hereinafter, but the invention should not beconstrued as being limited thereto.

EXAMPLE 1

As shown experimentally in the laboratory of the assignee, oneembodiment of a single liquid chamber device of the type described inFIG. 1 of the current invention delivers, as desired, HClO solutions ofconcentrations in the range 80-240 ppm chlorine at pH 5.9-7.8 as shownin Table 1. The operation of the electrosynthetic reactor relies on theuse of a DC constant current power supply connected to the GDE cathode(E-Tek ELAT® GDE LT250EW; 10 cm×10 cm) to induce reduction of dioxygento water and the oxidation of chloride ion at the DSA anode to generateHClO. Prior to connecting and turning on the power supply, theelectrosynthetic reactor is filled with either buffered or unbufferedNaCl solution from the gravity feed container and the flow rate adjustedwith a manual valve to 2-12 ml per minute. Both the HClO concentrations,as well as the pH of the effluent solution, are measured by conventionalinstrumentation and methods at various time intervals during continuousoperation, as a function of the flow rate, applied current and otherrelevant parameters.

TABLE 1 Hypochlorous Acid Generation in Electrolytic Cell NaCl Sol. FlowRate, Trial # ml/min DC Volts DC mA [Cl] ppm pH 5.0 g/L NaCl in pH 5.7,10 mM Phosphate Buffer 393-89-1 8 3 120 80 6.2 393-89-2 7 3 120 105 5.9393-89-3 a) 6 3.5 190 185 5.9 393-89-4 a) 6 3.5 170 195 5.9 393-89-5 b)10 3.9 250 160 6.2 393-89-6 b) 8 3.9 240 190 6.1 393-89-7 8.5 4.9 400230 6.2 393-89-8 7.5 4.9 380 225 6.2 5.0 g/L NaCl in Deionized Water393-89-9 7 3.9 270 170 6.5 393-89-10 10 3.9 250 170 8 393-89-11 c) 10.54.6 340 240 6 393-89-12 c) 10.5 4.6 320 190 7.2 393-89-13 c) 11 5 390210 7.8

In the present device, a method for the generation of hypohalous acidcomprising oxidizing halide ions in the presence of water within asingle liquid chamber to form an anolyte effluent is achieved. On thecathode side, oxygen is being fed through, or in the case of utilizing apump being forced through, a gas permeable cathode to reduce the oxygenin the presence of water to form hydroxyl groups. In this device the gaspermeable cathode forms at least a portion of an exterior wall of thesingle liquid chamber. The step of mixing the hydroxyl groups in anamount sufficient to complete the electrolyte circuit within the deviceto produce hypohalous acid is achieved. The pH may be determined by a pHmeter and the hypohalous acid may be removed from the electrolyticdevice. Control of pH may be attained by adjusting the current to thecircuit as applied by the DC constant current power or by adding abuffering agent to the halide aqueous feed. Desired range for use ashand sanitizer is pH between about 4 and 9. The step of feeding oxygento the gas permeable cathode may include delivering oxygen from a gascompartment, wherein the portion of the exterior wall of the singleliquid chamber comprised of the gas permeable cathode is included in thegas compartment. Alternatively, the step of feeding oxygen to the gaspermeable cathode may include exposing the hydrophobic exterior of thegas permeable cathode to atmospheric air.

A method of this invention utilizing a two liquid chamber electrolyticdevice for the generation of pH-controlled hypohalous acid aqueoussolutions, such as HClO in aqueous solution, is achieved. The methodincludes, on the anode side, oxidizing halide ions in the presence ofwater within an anolyte chamber to form an anolyte effluent containinghypohalous acid. On the cathode side, oxygen is fed through a gaspermeable cathode to reduce the oxygen in the presence of water to forma catholyte effluent containing hydroxyl groups, wherein the gaspermeable cathode forms at least a portion of an exterior wall of acatholyte chamber. The hydroxyl groups are mixed in an amount sufficientto complete the electrolyte circuit within the device to producehypohalous acid. This device allows for controlling pH of the hypohalousacid to ensure that the pH is between about 4 and 9. Determining the pHof the hypohalous acid may include use of a pH meter. The hypohalousacid may be removed from the electrolytic device.

The pH may be further controlled and regulated in the two liquid chamberelectrolytic device, for example, by mixing the exiting anolyte andcatholyte effluents in an amount sufficient to increase the pH of thehypohalous acid to ensure that the pH is between about 4 and 9. Themethod further comprises the step of determining the pH after mixing theexiting anolyte and catholyte effluents, wherein the step includes theuse of a pH meter. This method is advantageous in that the pH of thehypohalous acid produced may be controlled to ensure that the pH isbetween about 4 and 9 before removing the hypohalous acid for use as endproduct.

Regulating the pH of the hypohalous acid produced by the two liquidchamber electrolytic device may further be accomplished by recirculatingthe flow of the hypohalous acid back into the anolyte chamber if the pHof the hypohalous acid is above pH 9; wherein the method furthercomprises the step of determining the pH of the hypohalous acid afterrecirculating the flow of the hypohalous acid back to the anolytechamber, wherein the step includes the use of a pH meter.

In another embodiment, it will be appreciated that the user could alsoregulate the pH of the hypohalous acid produced by the dual liquidchamber of the electrolytic device if the pH is below 4 alternatively by(1) recirculating the flow of the hypohalous acid back to the anolytechamber where the input from the feed may also be altered of buffered or(2) closing off the valve 354 shown in FIG. 5 until the pH increasessufficiently above pH 4.

The step of feeding oxygen to the gas permeable cathode may includedelivering oxygen from a gas compartment, wherein the portion of theexterior wall of the catholyte chamber comprised of the gas permeablecathode is included in the gas compartment. Alternatively, the step offeeding oxygen to the gas permeable cathode may include exposing thehydrophobic exterior of the gas permeable cathode to atmospheric air.

The method and device of this invention further has the advantage inthat storage of gaseous species, such as chlorine gas, is not needed.Also, the source electrolyte is economical and safe for handling, whilethe end product may be directly used for disinfectant purposes at acontrolled pH level suitable for use as a hand sanitizer withoutirritation or damage to human skin.

In light of the foregoing, it should thus be evident that the process ofthe present invention, providing a device and method for producinghypohalous acid in aqueous solution with controlled pH, substantiallyimproves the art. While, in accordance with the patent statutes, onlythe preferred embodiments of the present invention have been describedin detail hereinabove, the present invention is not to be limitedthereto or thereby. Rather, the scope of the invention shall include allmodifications and variations that fall within the scope of the attachedclaims.

1. An electrolytic device for the generation of hypohalous acid inaqueous solutions, the device comprising: a single liquid chamber havingan inlet for receiving an aqueous solution containing halide ionstherein, the single liquid chamber having an exterior wall and a solidanode contained within the single liquid chamber providing for theoxidation of the halide ions to provide an aqueous solution ofhypohalous acid; and a gas permeable cathode forming at least a portionof the exterior wall of the single liquid chamber, the cathode providingfor the reduction of oxygen to provide hydroxyl ions in solution withinthe single liquid chamber to mix with the hypohalous acid produced atthe anode, the cathode having a hydrophobic surface for receiving oxygenfrom outside the single liquid chamber and a hydrophilic surface incontact with the electrolyte solution allowing for reduction ofdioxygen.
 2. The electrolytic device as claimed in claim 1, wherein thesingle liquid chamber further includes an outlet including a pH controldevice for determining the pH of the exiting mixed effluent.
 3. Theelectrolytic device as claimed in claim 1, wherein the hypohalous acidis hypochlorous acid and the halide ions are chloride ions.
 4. Theelectrolytic device as claimed in claim 1, further including a gascompartment for providing oxygen to the gas permeable cathode, whereinthe gas compartment is defined by at least one exterior wall thatencloses the portion of the exterior wall of the single liquid chambercomposed of the gas permeable cathode within the gas compartment.
 5. Theelectrolytic device as claimed in claim 4, wherein the gas compartmentincludes an inlet for receiving oxygen into the gas compartment.
 6. Theelectrolytic device as claimed in claim 1, wherein the solid anode is adimensionally stable anode.
 7. The electrolytic device as claimed inclaim 1, wherein the gas permeable cathode is a gas diffusion electrode.8. The electrolytic device as claimed in claim 2, wherein the pH controlfor determining the pH is a pH meter and sensor.
 9. An electrolyticdevice for the generation of hypohalous acid in aqueous solutions, thedevice comprising: an anolyte chamber having an inlet for receiving anaqueous solution containing halide ions therein, the anolyte chamberhaving an exterior wall and a solid anode contained within the anolytechamber providing for the oxidation of the halide ions to provide ananolyte effluent of hypohalous acid in aqueous solution; a catholytechamber having an inlet for receiving an aqueous electrolyte, whereinthe catholyte chamber is defined by at least one exterior wall orportion thereof comprising a gas permeable cathode, the cathode having ahydrophobic surface for receiving oxygen from outside the catholytechamber and a hydrophilic surface allowing for reduction of dioxygen;and an ionomeric membrane for partitioning the anolyte chamber from thecatholyte chamber; wherein the anolyte chamber further includes anoutlet including a pH control for determining and regulating the pH ofthe exiting anolyte effluent to between about 4 and
 9. 10. Theelectrolytic device as claimed in claim 9, wherein the catholyte chamberincludes reacted catholyte effluent therein.
 11. The electrolytic deviceas claimed in claim 10, wherein catholyte chamber includes an outlet forreleasing any reacted catholyte effluent remaining in the catholytechamber to mix with the exiting anolyte effluent.
 12. The electrolyticdevice as claimed in claim 11, wherein the pH control for regulating thepH includes a valve and a recirculator for recirculating the flow of theexiting mixed anolyte and catholyte effluents back into the anolytechamber when the mixed anolyte and catholyte effluents have a pH that isgreater than
 9. 13. The electrolytic device as claimed in claim 9,further including an inlet valve for releasing a buffering agent intothe anolyte chamber of aqueous solution containing halide ions.
 14. Theelectrolytic device as claimed in claim 9, wherein the pH of the mixedanolyte and catholyte effluents is regulated between about 5 and
 8. 15.A method for the generation of hypohalous acid comprising: oxidizinghalide ions in the presence of water within a single liquid chamber toform an aqueous solution of hypohalous acid; feeding oxygen through agas permeable cathode to reduce the oxygen in the presence of water toform hydroxyl ions, wherein the gas permeable cathode forms at least aportion of an exterior wall of the single liquid chamber; mixing thesolution containing hydroxyl ions in an amount sufficient to completethe electrical circuit within the device and to produce hypohalous acid;determining the pH of the hypohalous acid to ensure that the pH isbetween about 4 and 9; and removing the hypohalous acid.
 16. The methodof claim 15, wherein the step of determining the pH of the hypohalousacid includes the use of a pH meter.
 17. The method of claim 15, whereinthe step of feeding oxygen to the gas permeable cathode includesdelivering oxygen from a gas compartment, wherein the portion of theexterior wall of the single liquid chamber comprised of the gaspermeable cathode is included in the gas compartment.
 18. A method forthe generation of hypohalous acid comprising: oxidizing halide ions inthe presence of water within an anolyte chamber to form an anolyteeffluent containing hypohalous acid; feeding oxygen through a gaspermeable cathode to reduce the oxygen in the presence of water to forma catholyte effluent containing hydroxyl ions, wherein the gas permeablecathode forms at least a portion of an exterior wall of a catholytechamber; mixing the solution containing the hydroxyl ions in an amountsufficient to complete the electrical circuit within the device toproduce hypohalous acid; controlling the pH of the hypohalous acid toensure that the pH is between about 4 and 9; and removing the hypohalousacid.
 19. The method of claim 18, wherein the step of controlling the pHof the hypohalous acid further includes the steps of determining the pHof the hypohalous acid and regulating the pH of the hypohalous acid. 20.The method of claim 19, wherein the step of determining the pH of thehypohalous acid includes the use of a pH meter and sensor.
 21. Themethod of claim 19, wherein the step of regulating the pH of thehypohalous acid further includes mixing the exiting anolyte andcatholyte effluents in an amount sufficient to increase the pH of thehypohalous acid to ensure that the pH is between about 4 and
 9. 22. Themethod of claim 21, further comprising the step of determining the pH ofthe hypohalous acid after mixing the exiting anolyte and catholyteeffluents, wherein the step includes the use of a pH meter.
 23. Themethod of claim 21, wherein the step of regulating the pH of thehypohalous acid further includes recirculating the flow of thehypohalous acid back to the anolyte chamber if the pH of the hypohalousacid is below 4 or above
 9. 24. The method of claim 23, furthercomprising the step of determining the pH of the hypohalous acid afterrecirculating the flow of the hypohalous acid back to the anolytechamber, wherein the step includes the use of a pH meter and sensor. 25.The method of claim 18, wherein the step of feeding oxygen to the gaspermeable cathode includes delivering oxygen from a gas compartment,wherein the portion of the exterior wall of the catholyte chambercomprised of the gas permeable cathode is included in the gascompartment.